Process for the electrochemical fluorination of organic acid halides

ABSTRACT

A process for the electrochemical fluorination of organic acid halides is provided. The electrochemical process is carried out in liquid hydrogen fluoride as electrolyte containing 5 to 20 percent by weight based on the electrolyte of the acid halide, at temperatures of 20* to 50*C, optionally under pressure and at a cell voltage of 9 to 15, preferably of 9 to 13 volts direct current. The anodes used are of nickel or a nickel alloy while the cathodes are e.g. of iron or steel and the distance between the electrodes is about 6 to 12 mm. According to this process perfluorinated compounds of high purity and in good yields are obtained. These compounds are useful as surfactants or as intermediates for the manufacture of surfactants, oil- and waterrepellents lubricants and the like.

United States Patent 1 Plattner et al.

Hfil Nov. 11,1975

[75] Inventors: Eric Plattner. Seltisherg; Christos Comninellis. Prilly. Philippe Javet. Eeuhlens. ull ol- Switzerland [73] Assignee: Ciha-(leigy AG. Busel. SWIUCTILIHd (22 Filed: Sept. 9 I974 [II I Appl. No.1 504.581

[30] Foreign Application Priority Data Sept ll. I973 Snit/erlnnd... M10617} [52] US. Cl. 204/59 F [5 I] Int. CL CZSB 3/08 [58] Field of Search 204/59 F [56] References Cited UNITED STATES PATENTS 2.5 IIHI-U WIUFII Snnons ZIH/(vl 2.? l INTI )lll55 SCIIIIIIIQI'LL el 104/5) F 1.733.398 Illlio Brice et til I. Zoo/5o knoll-I33 HAIF I Holland et til... BIN-I59 F FOREIGN PATENTS OR APPLICATIONS 1.458.234 I ZIIWI iermun OTHER PUBLICATIONS Grumstzid et ul.. J.C.S.. I956. pp. 173481). Grumstud et Lll.. J.C.S.. I957. pp. 1640-1645. Bordon et ul. J.C.S.. I957. pp. 25744575.

lri'nuu'y I-..\uminurR. L. Andrews Attorney. Agent. or l-irm-Joseph G. KUIULII1 \L Pruhodh I. Almuulu; Edward MeC. Roberts I57 ABSTRACT A process for the eleetroehemieul fluoritmtion of orgunic ueid halides is provided The eleetroehemieul process is curried out in liquid hydrogen fluoride us eleetrolyte eontuining 5 to 20 percent h eight Imsed on the electrolyte ol the acid hulide. LII temperatures of 20 to 50C. optionull under pressure and LII u eell \oltuge of to I5. preleruhl of 9 to I3 \olts direet current. The unodes used are of nickel or u nickel zillo while the cathodes 'tlre e.g. of iron or steel and the LIISILlIlCC between the electrodes is about h to II min. According to this process perl'luorinuted eon]- pounds olhigh purit und in good \ieltls tire ohtuined These compounds are useful as surllietunts or us inter mediates for the manufacture of surllletunts oiland \VLIICF-I'CDCIICITIS Iuhrieunts und the like.

14 Claims. N0 Drawings PROCESS FOR THE ELECTROCHEMICAL FLUORINATION OF ORGANIC ACID HALIDES Processes for the manufacture of fluorocarbon compounds are already known. U.S. Pat. No. 2,519,983 describes the electro-chemical manufacture of fluorocarbon compounds at a cell voltage of about 4 to 8 volts direct current. a current density of up to about 20 m A/cm and at a temperature of 20C to +80C, preferably C to +20C, in liquid hydrogen fluoride as electrolyte. The application of a higher voltage is not recommended since energy is lost and at the same time no improvement in yield is attained. Further, long-chain carbon compounds are more highly fragmented simultaneously with the addition of fluorine, i.e. a great number of compounds with a lower number of carbon atoms than those of the starting compound are formed. The electrochemical fluorination of carboxylic acid halides and sulphonic acid halides forms the subject matter of U.S. Pat. Nos. 2,717,871 and 2,732,398. The conditions for carrying out the process correspond to the stated values, i.e. the process is carried out for example at a cell voltage of about 4 to 6 volts direct current. Likewise only unsatisfactory yields are obtained with long-chain starting products, since molecular fragmentation. optionally combined with cyclisation reactions, occur during the reaction. Consequently, the yields of trifluorometlianesulphochloride are about 55% (T. Gramstead and R. N. Hazeldine, J.C.S. 173 l956) report 96 and of perfluorooctanesulphochloride 25 [cf. T. Gramstead and R. N. Hazeldine, J.C.S. 2640 (1957)], whereas J. Burdon et al., J.C.S. 2574 (1957) obtain only about l2 to A further process for the electrochemical fluorination is known from German Auslegeschrift No. 1468284. By the choice of the starting compounds, the attempt is made to improve both the selectivity of the electrochemical reaction and the yield. The process, which is carried out under the cited conditions (potential of about 4 to 8 volts), is confined to a special group of starting compounds some of which are not readily accessible. The yields are only good in respect of shortchain molecules, whereas e.g. in the manufacture of C F SO F only yields of less than were obtained.

The present invention provides an improvement of the process for the electrochemical fluorination of organic acid halides, in particular of long-chain acid halides, by using in contrast to the prior art a substantially higher cell voltage while at the same time optionally increasing the current density. The temperature range for carrying out the electrochemical fluorination has also been modified. Surprisingly, the yield of fluorinated acid halides and the purity of the end products are substantially improved in the process according to the invention while at the same time improving the current yield. The formation of molecular fragments with fewer carbon atoms than the starting material, the occurrence of any side reactions and the formation of only partially fluorinated products can be very largely avoided. Further, the corrosion of the anode material is materially reduced.

The present invention therefore provides a process for the electrochemical fluorination of organic acid halides using an anode of nickel or a nickel alloy, a metal cathode and liquid hydrogen fluoride as electrolyte, which comprises electrolysing organic acid halides, optionally under pressure, and at temperatures of 20C to 50C, at a cell voltage of 9 to 15 volts direct current. and subsequently separating the fluorinated products from the electrolyte.

Suitable organic acid halides are normally alkylcarboxylic acid and alkylsulphonic acid halides with 5 to 18. preferably 6 to 12 or 8 to 10. carbon atoms in the alkyl moiety. Acid chlorides and, in particular. acid fluorides are preferred. They have e.g. the formulae 1. CH (CH COX and 2. CH (CH SO X. wherein X represents fluorine, chlorine or bromine, m is an integer from 3 to 16, preferably from 4 to ID or 6 to 8, and n is an integer from 4 to l7. preferably from 5 to l l or 7 to 9. Preferred acid fluorides are also those of the formulae 3. CH (CH COF and 4. CH (CH SO F wherein m is an integer from 4 to 10, preferably 6 to 8, and n is an integer from 5 to l l, preferably from 7 to 9.

Examples of organic acid halides are hexanoic-, octanoic-, decanoicor dodecanoicsulphonic acid halides, in particular the sulphonic acid fluorides.

These acid halides are mixed with the liquid hydrogen fluoride in an amount of about 5 to 20, preferably 5 to 15 or l0 to l5 by weight before the start of the electrochemical fluorination. Commercial anhydrous liquid hydrogen fluoride which normally contains a trace of water is used as electrolyte. ln contact with a humid atmosphere, the hydrogen fluoride moreover takes up water. The bulk of this water can be removed by a preliminary electrolysis that is carried out before addition of the starting materials. The water is removed by hydrogen. oxygen and oxygen fluoride (05), all of which escape in gaseous form. It is not necessary to add conductivity salts, e.g. potassium fluoride, to the electrolyte, since this causes increased corrosion of the electrode material. Moreover, the electrolyte retains its conductivity, even after termination of the fluorination, so that the conclusion of the reaction is only inadequately detected.

The electrochemical fluorination is carried out at temperatures between 20C and 50C, preferably between 30C and 40C. The best yields are obtained at about 30C to 35C. The process is ordinarily carried out at normal pressure or at an overpressure of up to about 5 bar, preferably up to about 1 bar.

The cell voltalge is 9 to 15, preferably 9 to 13 or 9 to 12 volts wihtout any development of fluorine gas being observed. The voltage theoretically necessary for the manufacture of free fluorine (F from hydrogen fluoride is about 3 volts (U.S. Pat. No. 2,519,983). If it is possible to apply higher voltages without the development of fluorine gas according, the reason is that a substantial amount of the voltage is used up for overcoming the resistances that are formed through the electrolyte, the electrodes and especially through polarisation effects at the electrode surfaces.

The electrodes are spaced about 6 to 12, preferably 8 to 10 mm apart. These relatively large spacings made it possible for example to markedly reduce the corrosion of the electrodes and the danger of a short-circuit reaction between the electrodes.

The current densities can be in the approximate range from ID to I00 mA/cm preferably in the range from 20 to 60 mA/cm whereby it is possible to attain current yields of over 50 Although the reaction mechanism has not been fully clarified and the present invention is not limited by any specific reaction mechanism. it is assumed that in the electrochemical fluorination described herein a loose. active complex of different nickel fluorides and molecular or atomic fluorine is first formed at the anode. The acid halide adsorbed on the complex is then completely reacted, then the current densitiy falls to a fraction of the initial value and thereby indicates the end ofthe electrochemical fluorination.

Support for this possible reaction mechanism is to be found in the fact that practically no partially fluorinated products are formed and that there is no visible formation of fluorine gas. since free fluorine (F from the active complex can also be used for the fluorination. It can further be observed that the corrosion of the anodes (after an induction period using new anodes) is very slight, which can be attributed to the formation of a protective layer of nickel fluorides.

Preferably nickel or a nickel alloy is used as anode material for the process according to the invention; but optionally it is also possible to use anodes of silicon carbide or charcoal. Suitable cathodes are iron or steel cathodes. also those of e.g. aluminium, copper. nickel or nickel alloys.

The electrochemical fluorination can be carried out batchwise and optionally also semibatchwise by replenishing both the organic compound and the hydrogen fluoride electrolyte from time to time in the same amount in which they are used up and separating the perfluorinated products which are insoluble in hydrogen fluoride from the electrolyte and removing them from the cell.

The escaping gas mixture can be led through an ascending cooler in order to condense the hydrogen fluoride vapours. then after dilution with an inert gas it is absorbed in dilute sodium hydroxide solution.

experiment I The perfluorinated compounds obtained are valuable starting materials for the manufacture of oil and water repellents, surfactants. lubricants and the like. The end products are obtained by modification the acid halide grouping by known chemical reactions. Further. they can also be used by themselves as surfactants.

The following Examples describe the invention in more detail but do not limit it to what is described therein.

EXAMPLE 1 Manufacture of perfluorooctylsulphonic acid fluoride The reaction is carried out in an electrolysis cell of nickel with a capacity for ml ofliquid hydrogen fluoride and provided with a nickel anode (0.35 dm surface area). a thermometer, an inlet pipe for the acid halide and the liquid hydrogen fluoride as well as an exhaust gas pipe cooled to l5C which is sparged with nitrogen in order to prevent the formation of explosive gas mixtures and to produce a desired pressure (under which the electrochemical reaction proceeds) in the cell. The cell is in a thermostat. At the start of the reaction, the cell is cooled to +10C, then the liquid hydrogen fluoride (-IOC) and octanesulphonic acid fluoride are charged into the cell.

The cell is then heated with the thermostat to the desired temperature. The nitrogeapiessure is about 0.6 bar overpressure at 35C. Upon te 'rtuination of the reaction, the cell is again cooltdi 0' a temperature of +l0C and brought to normal pmswre. The fluorinated reaction product is insoluble inlilqaid hydrogen fluoride and precipitates as a colourless oil on the bottom of the cell. The oil is isolated washed with 10 aqueous sodium hydrogen carbonate solution. The purity of the product is normally 90 to 95 (analysis by gas chromatography). The indicated yields are calculated on the oily end product with a content of at least 90 perfluorooctylsulphonic acid fluoride. The following table contains the test conditions and results:

(comparison example) temperature (C) 32 amount by octanesulphofluoride 4 (g) concentration in 9? (relative to the electrolyte) potential volt 9 current consumption A/h (actual) current consumption referred to the theoretical value (5%) current yield (9%) product yield (g) 3.4

-continued product yield ("/r) 41 43 47 (ii Experiment 6 was carried out under the conditions of the prior art. The yield obtained is markedly lower than the yields that are obtained with the process according to the invention.

EXAMPLE 2 Perfluorination of n-heptane-l-carboxylic acid fluoride (octanoic fluoride) At C. 20 parts of anhydrous hydrogen fluoride are charged into the electrolysis cell according to Example I and then 3 parts of n-heptane-l-carboxylic acid fluoride are added thereto. The contents are electrolysed under a nitrogen over-pressure of 1 bar at 30C, a cell voltage of IO volts and an initial current density of 0.037 A/cm The electrolysis is discontinued when 80 of the theoretical amount of current has been consumed.

Yield: 2.65 parts of a crude oil with 87 content of perfluorinated compound. The oil is purified as described in Example 1. The yield is 37 of theory.

We claim:

I. A process for the electrochemical fluorination of organic acid halides using an anode of nickel or a nickel alloy, a metal cathode and liquid hydrogen fluoride as electrolyte, which comprises clectrolysing the organic acid halides in an amount of 5 to 20 percent by weight. based on the electrolyte, at temperatures of 20C to 50C, at a pressure of from normal pressure to an overpressure of about 5 bar, and at a cell voltage of 9 to volts direct current and a current density of to 60 mA/cm, the distance between the electrodes being 6 to 12 mm. and subsequently separating the fluorinated products from the electrolyte.

2. A process according to claim I, which comprises electrolysing organic acid halides of the formulae CH (CH COX and wherein X represents fluorine. chlorine or bromine. m is an integer from 3 to I6 and n is an integer from 4 to 17.

3. A process according to claim 2, which comprises the use of organic acid fluorides of the formulae CH3 )m and CH (CH SO F wherein m is 4 to [0, and n is 5 to 11.

4. A process according to claim 3, which comprises the use of octanesulphonic fluoride or octanoic fluoride.

5. A process according to claim 3, wherein m is 6 to 8andnis7to9.

6. A process according to claim 2, wherein the distance between the electrodes is 8 to [0 mm.

7. A process according to claim 1, wherein the amount of the acid halides is 5 to 15 percent by weight, based on the electrolyte.

8. A process according to claim 7 wherein the amount of the acid halides is [0 to 15 percent by weight, based on the electrolyte.

9. A process according to claim 1, wherein the fluorination is carried out at temperatures of 30C to 40C.

10. A process according to claim 9, wherein the fluorination is carried out at temperatures of 30C to 35C.

ll. A process according to claim I. wherein the fluorination is carried out at a cell voltage of 9 to 13 volts.

12. A process according to claim I, wherein the fluorination is carried out at a cell voltage of 9 to 12 volts.

13. A process according to claim I, wherein the fluorination is carried out at normal pressure or at an overpressure of up to l bar.

14. A process according to claim I, which comprises adding the organic acid halides to the electrolyte semibatchwise and separating the insoluble perfluorinated products from the electrolyte.

4' i i l UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO.: 3,919,057 DATED November 11, 1975 INVENTOR(S) 1 ERIC PLATTNER ET AL it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column i, Example 1, in the Table at the bottom of the line 13 should read 0.025 0.020 0.050 0.056

line 16, delete "A/h" and insert Ah Line 19, delete "Dr/h" and insert Ah line 25 should read 3.4 3.6 3.9 5.1 4. 8 2.5

Signed and Scaled this [SEAL] fif D f June 1976 A Hes r:

RUTH C. MASON C. MARSHALL DANN Arresting Offirrr (ommiser'mier nfParenls and Trademarks 

1. A process for the electrochemical fluorination of organic acid halides using an anode of nickel or a nickel alloy, a metal cathode and liquid hydrogen fluoride as electrolyte, which comprises electrolysing the organic acid halides in an amount of 5 to 20 percent by weight, based on the electrolyte, at temperatures of 20*C to 50*C, at a pressure of from normal pressure to an overpressure of about 5 bar, and at a cell voltage of 9 to 15 volts direct current and a current density of 20 to 60 mA/cm2, the distance between the electrodes being 6 to 12 mm, and subsequently separating the fluorinated products from the electrolyte.
 2. A PROCESS ACCORDING TO CLAIM 1, WHICH COMPRISES ELECTROLYSING ORGANIC ACID HALIDES OF THE FORMULAE
 3. A process according to claim 2, which comprises the use of organic acid fluorides of the formulae CH3 (CH2)m COF and CH3 (CH2)n SO2F wherein m is 4 to 10, and n is 5 to
 11. 4. A process according to claim 3, which comprises the use of octanesulphonic fluoride or octanoic fluoride.
 5. A process according to claim 3, wherein m is 6 to 8 and n is 7 to
 9. 6. A process according to claim 2, wherein the distance between the electrodes is 8 to 10 mm.
 7. A process according to claim 1, wherein the amount of the acid halides is 5 to 15 percent by weight, based on the electrolyte.
 8. A process according to claim 7 wherein the amount of the acid halides is 10 to 15 percent by weight, based on the electrolyte.
 9. A process according to claim 1, wherein the fluorination is carried out at temperatures of 30*C to 40*C.
 10. A process according to claim 9, wherein the fluorination is carried out at temperatures of 30*C to 35*C.
 11. A process according to claim 1, wherein the fluorination is carried out at a cell voltage of 9 to 13 volts.
 12. A process according to claim 1, wherein the fluorination is carried out at a cell voltage of 9 to 12 volts.
 13. A process according to claim 1, wherein the fluorination is carried out at normal pressure or at an overpressure of up to 1 bar.
 14. A process according to claim 1, which comprises adding the organic acid halides to the electrolyte semibatchwise and separating the insoluble perfluorinated products from the electrolyte. 